1. Field of the Invention
The present invention relates to an apparatus using microwave and particularly, to a microwave sealing structure, capable of preventing leakage of microwave to the outside of a cavity where electron wave resonates.
2. Description of the Background Art
FIG. 1 is a perspective view showing a composition of a conventional microwave oven.
Generally, as shown in FIG. 1, a microwave oven includes a microwave energy source (not shown) and a resonator 1. The resonator 1 includes a cavity 2 having an opening 2A and a door 5 which can open and close the opening 2A. When the door 5 is closed, a gap exists between the cavity 2 and a door 5 and this gap basically forms a slot waveguide for leaking microwave energy from the resonator 1.
FIG. 2 is an enlarged cross-sectional view of A portion in FIG. 1 and FIG. 3 is a partial cut-away view showing a rim 5A of a door of the microwave oven of FIG. 1.
To prevent such leakage of microwave energy, microwave ferrite rubber is used for the door 5 of the microwave oven or a microwave sealing choke 7 is mounted around the door 5 or opening 2A as shown in FIGS. 2 and 3. Here, reference numeral 6 designates a choke cover which is non-conductive and covers the choke 7 and reference numeral 2B designates a rim surface of the opening 2A.
The microwave sealing choke is formed by having a distributed parameter choke of quarter wave and efficiently seals fundamental wave that microwave energy is leaked from the resonator of a microwave oven.
There are some examples that sealing of harmonics as well as the fundamental wave are considered. One of the examples is a multi-mode sealing choke disclosed in the U.S. Pat. No. 4,659,891. However, generally, a complicated structure is necessary to cover the harmonics.
As an example of the multi-mode microwave sealing choke for preventing leakage of microwave energy in the slot waveguide which is formed between the door and cavity of the microwave oven, there is a multi-mode microwave sealing choke having composite advantages in designation, which is disclosed in a thesis presented by S. Ohkava, H. Watanave and K. Kane, “High Resonance Door Seal for Microwave Oven” (Microwave Power Symposium Digest, 1978).
The multi-mode microwave sealing choke is installed in the quarter wave choke along a predetermined line that a series of LC circuits which are combined to each other strongly, cross the wave vector of microwave to be sealed and at the same time, a parallel LC circuit is installed in the quarter wave choke.
The two quarter chokes are combined with the slot waveguide through the combining hole. The LC circuits are composed of distributed parameter circuits.
However, the structure of the above composition is very complicated and the size is too large. Mass production is difficult. The direction of the technical development of the door of the microwave oven has been how a door with an improved performance can be miniaturized and embodied with a lower price.
On the other hand, the conventional microwave sealing structure can be described with reference to the U.S. Pat. Nos. 4,584,447, 4,742,201, 4,645,892 and the like.
In the U.S. Pat. No. 4,584,447, it is shown that an impedance inversion can be occurred in a shorter distance than the conventional quarter wave sealing choke. However, with the structure, mass productivity is decreased and has a mechanically frail structure. In terms of the performance, the structure has an excellent characteristic only in a wave incidence angle of a limited extent.
As an improved structure, there is a microwave sealing structure which is disclosed in the U.S. Pat. No. 4,742,201. However, the structure was not changed much but improving the mass productivity and mechanical strength at a certain degree.
The microwave sealing structure which is disclosed in the U.S. Pat. No. 4,645,892 is a structure which substantially improves the mass productivity of the door by making a hole of a screen with a steel plate and die cutting the portion to be bent in advance, differently from the conventional method.
However, the whole size of the structure is increased since the structure requires about half wave distance from the starting point of the gap inside the cavity to a short wall. Also, the structure shows an excellent characteristic only in a wave incidence angle of a limited extent.
On the other hand, the conventional microwave sealing structure for preventing leakage of the microwave energy was a sealing structure with a concept of a choke, that is, a concept for cutting off the transmission line by forming a distributed circuit of a quarter wave in a line of the transmission line.
Therefore, the sealing characteristic of a wide range of wave incidence angle was not good and to improve the performance, the structure became complicated.
Also, there was a limit for designing the microwave sealing structure small since the size of the choke is related to the wavelength of the microwave, that is, the length.
Therefore, in the conventional microwave sealing apparatus of the microwave oven, a proper structure to be commercially applied to a microwave oven is not disclosed and the manufacturing is complicated due to the structure.